Signaling system



. Nov. 26; 1940.

N. F. SHOFSTALL SIGNALING SYSTEM Filed Feb. 1, 1938 Inventor: Norton F. Shofstal I,

His Attorney.

Patented Nov. 26, 1940 SIGNALING SYSTEM Norton F. Shofstall, Stratford, Conn., assignorto General Electric Company, a corporation of New York Application February 1, 1938, Serial Nb. 138,083

13 Claims. (Cl. 250-27) My invention relates to signaling systems and more particularly to an arrangement for regulating the voltage supplied thereto. In greater particularity, my invention relates to a method of an arrangement for maintainingconstant the voltage supplied to thermionic devices employed in a signaling apparatus.

It is highly desirable and often quite indispens-v able in the operation of signaling apparatus utilizing thermionic devices that the voltage of the several energizing sources shallremain' substantially constant. This is especially true with regard to the space current source for thermionic devices which perform certain functions, typicalof which are oscillators and converters where it has been found that a change in anode potential of one volt results inv a change in frequency of two hundred cycles at fifteen megacycle operation. Certain types of signaling arrangements,

as, for example, radio receivers employing automatic volume control, experience during a period of normal operation a comparatively large fiuotu ation in the space current consumed by certain of the thermionic tubes. If the radio receiver has in addition to automatic volume control a thermionic frequency converter tube operating at high frequencies, this fluctuation is likely to create a corresponding variation in'the anode voltage, caused by an inherently poor regulation of the anode supply, which may seriously impair the operation of the converter and thereby greatly impair the usefulness of the receiver.

It is accordingly an object of my invention to overcome these undersirable fluctuations in the terminal voltage of the space current supply by the provision of a regulating system which will maintain substantially constant the space current consumption of the thermionic devices and thereby maintain correspondingly constant the terminal voltage of the energizing source.

A further object of my invention is to attain this result by utilizing to a large extent apparatus already present in the signaling system whereby a minimum of additional equipment is required and a greatly improved operation results.

A still further object ,of my invention is so to arrange the circuit and the bias of an electronic tuning indicator control device that decreasing 5 values of received signal intensity will result in decreasing values'of space current in this device equal in amount to the increasing values of current consumed by certain of the other thermionic devices caused by the same change in signal int ns A further object of my invention is so to arrange the circuit of a radio receiver provided with automatic. volume control and thermionic tuning indication that the change in space current of certain of the thermionic tubes caused by-the operation of the automaticvolume control is compensated by an opposite change of equal or proportionate amount in space current consumption by the thermionic tuning indication device. I m I n additional object of my invention is to maintain. the potential of an energizing source constant by an arrangement which operates entirely'automatically to control the value of our-'- rent' consu med by ,two or more of the thermionic 15 devices whereby a changing condition whichproduces an increasein the current consumption by one device will produce a corresponding and opposing change of equal or proportional'amount in the current consumption of another device. 20

The novel; features which I believe to be characteristic 'of: my invention are set forth with particularity in the appended claims. My inven-. tion itself, however, both as to its organization and' method ofoperation together with further 25 objects and advantages thereof, may best be understood by reference to the following description taken in, connection with the accompanying drawing in which Figure '1 represents an embodiment of myinvention, and Figure 2 repre- 30 sents a modified. embodiment thereof.

Referring to the drawing, I have illustrated in Fig l a radio receiving system having an antenna I connected to ground through the primary-2 of a radio frequency transformer 3. The 5 secondary 4 of the transformer, tuned by a variable condenser 5 to the frequency of a desired signal, is connected to the control grid 6 and the cathode l of a radio frequency amplifier tube 8. The-anodeSof this amplifier is connected through the primary H] of a radio frequency transformer H and a conductor 12 to the positive pole l3 of the space current source connected between the terminals I3 and l4. Bleeder resistors l5, I6, 11' and I8 are connected between the terminals I3 45 and; to supply reduced potentials to various portions of the set in conventional manner. A connection l9 to ground is made between the resistors 16 and I1. The suppressor grid 2001: the amplifier tube 8 is connected to the cathode I while the screen grid 2| is connected to a point of reduced space current supply potential between the bleeder resistors IS'and l6.

Thesecondary 22 of the transformer ll is tuned.

to the desired signal frequency by, a variable condenser 23 arranged for uni-control with the condenser 5, and signal oscillations appearing across this tuned circuit are impressed between the cathode and the control grid of a converter stage 24. The converter 24 has connected to an oscillator and anode grids therein in conventional manner a circuit comprised by the inductively coupled windings 25 and 26. The winding 26 is tuned by avariable condenser 21,

arranged for uni-control with the condensers 5 g and 23, to a frequency differing by a fixed amount -sumptioncauses a corresponding and opposite from the frequency of the signal oscillation;

The converter 24 operates to change the f-re- 1 tween the terminals l3 and UL Any change in quency of the signal oscillation appearing across the tuned circuit'22, 23 to an intermediate frequency oscillation and supplies these oscillations .to an intermediate frequency 'amplifierfrepie" sented conventionally at 28 which may consist of any desired number of stages of amplification. The intermediaite frequency amplifier '28' termina'tesin'a channel 29' connected to theprimary'3 l of an output transformer'32 which is tuneol by the respective variable condensers "33 and-1 3 i to the intermediate frequency.

Intermediate frequency oscillations appearing in the secondary' 35 of the transformer 32 are rectified by; the diodeelements 36ofan electron discharge device" 31 to provide a unidirectional electromotive force across a resistor 38 an'dparallel' connected condenser 39.- This electromotive forceywhich is the audio frequency component of: the signal oscillation, is connected through the conductors it; and M"- and through a coupling condenser to the input of a conventional audio frequency amplifier, not shown, whereit is amplifiedand reproduced in a manner well known. A second portion of the intermediate frequency is cupled "through a condenser 43 to the diode elements M of theel'ectron discharge device'3'l and through aconductor 45-and a resistor 46 to a'pointlbetween the bleeder resistors H and I8. The resistors 46 and I1 are thus'connected in parallel y'with the-"diode elements 44 and have built up thereacross a pulsating. unidirectional electroi'notiveforce for purposes of automatic volumecontroh This electromotivexforce is connectedzthrough afilter comprised. by a resistor 5 4:1". and a 'con'densen lla. and through the control circuit '43 to. thelcontrolgridof such radio fre.--

quency-andintermediate frequency stages of amplificationas may be desiredto provide with con- 7 ventionalautomatic-volume control. 55 scribed will now be. evident. Signal oscillations appearing in the antenna. I are coupled through the transformer}; to the radio frequency amplifier; 8.; where they are amplified and coupled 62) through the transformer H to the converter stage 2 4 The signal oscillations are here changed to an. intermediate frequency oscillation and are then passed to theintermediate. frequency amplifier 28 for further amplification. The .amplified intermediate frequency oscillations are coupledthrough the transformer 32 to thediode'elements 36 where they are rectified and the audio frequency components of rectification are translj ferred-through the condenser 42 to the audio fref7'0 quency amplifier for further amplification and reproduction. A second portion of the intermediatefrequency oscillations arerectified by the diode elements 44130; provide automatic vol- .1, ninecontrol voltage; in; the conductor, 48. This control voltage operates in a manner well known terminal I 3.

oscillations appearing in the signal channel 39 l he, operation of the arrangement thus far dein the art to maintain the intermediate frequency oscillations appearing in the output of the intermediate frequency amplifier 28 of substantially constant amplitude.

The action of the automatic volume control circuit in variably biasing the grid element of those amplifier stages to which it is connected results in a variation of the space current in these stages with'variationof received signal intensity. If the supply connected to the terminals l3 and I4 is such 'as to have a relatively poor regulation, this variation in'space current convariation in the terminal potential appearing beauxiliaryelectronic discharge device. such as the electronic tuning. indicator control tube 49. The tube 49has a groundedcathodefifl, acontrol. grid 5| connected through a resistor522 to that end of the resistor 38"whi-ch is connected to the diode element, and: an anode 53. connected through the saturating windingfi l of a saturable core reactor 55' andx'conduoton'fi to the space current supply 55 to an incandescent lamp 58" having a distinc tive color, as for example the color green. A second incandescent: lamp 59 is connectedacross the winding 5'7, this lamp also having a distinc tive color, asfor example the colorred, different T from that of lamp-58 A'voltage limiting resistor 60 is connected across-the terminals of theincandescentlamp 58 fora purpose shortly to become apparent. This-arrangement of the electronic device 49, the reactor 55, and the lamps 5'8 and 59 operates in a manner as follows.

The other end. of the resistor 38 In the; absence of signal oscillations in the signal channel 29, the electronicdevice 49 is ;biased to cut-ofi as-explained above, and no-anode cur-. rent thereforefiows in thesaturating winding '54.

The impedance ofv the winding 51 under this condition is a maximum with the result that a pe tential drop occurs across the terminals of. the lamp 59 which, by prcperiselection'of the value of the resistor fl, may be a large proportion of the total voltage impressed across the terminals Bl. Ihe illumination from the red lamp 59 then predominates o'verthat from the green lamp 53.

Upon the occurrence of'a .signalfoscillation in the signalichannel 29, a unidirectional pulsating voltage isdeveloped by the diode elements 36 across the resistor 38 wane polarity tending to decrease the negative bias on the control grid 5| of the device 49: Space current now begins to flow in thedevicedfi. and the core of the reactor 55 is saturated to a degree depending upon the magnitude of the spacev current. An increase in the core. saturation results in a decrease in the value of the impedance of the winding 57 which, by its shunting effect on the lamp 59, in' turn causes a greater proportion of the potential drop ofthe source connected to the terminals 6| to be impressed across the terminals'of the green col-' cred-lamp 58. The illumination of the green lamp now increases and may, with a sufficient space current flowing in the device 49, eventuallypredominate over that of --the red lamp 59, the illumination of which-is decreasing as the reactance of the winding 51- decreas'esp This arrangement ofthe lamps 58 and 59 constitutesan indicator for indicating the presence and relative strength or the absence of a signal'inthe signal channel. I

A little further refiection'will make evident the 2 to which this circuit is connected in proportion to the amplitude of the signal oscillation. The same signal likewise and simultaneously causes a control potentialin the control circuit 40 which operates to increase the space current of the electronic discharge device 49 in proportion to the amplitude of the signal oscillation. If the space current in the device 49 increases as rapidly as the space currents in the several amplifying stages to which the automatic volume is connected decrease, the space current load on the source connected between the terminals l3 and 14 remains constant and the potential across the terminals l3 and I4 also remains constant irrespective of the regulation of the supply source. The suitable choice of an electronic discharge device 49 to accomplish this result in practice depends in large part upon a choice of the other thermionic devices used for radio and'intermediate frequency amplification and upon the number of stages automatically controlled. A proper 45 choice may be made by one skilled in the art.

Thepotential of a point on the bleeder resistor may be maintained constant in similar manner by connecting the conductor 56 to-that point and by suitably adjustingthe bias on the operating grid 5| of the device 49 to cut-01f. Thus the potential applied to the screen grid of the several electronic discharge devices used in the signaling apparatus may be maintained substantially constant by connection of the conductor 56 to a point between the resistors l5 and I6 and by suitably choosing a value for the resistors l1 and I8 to bias the device 49 to cutofi.

A modification of my invention is shown in Figure 2 wherein I have indicated elements corresponding to like elements of Figure 1 by like numerals. This modified arrangement, which provides an alternative method for biasing the 5 control grid 5| of the device 49, allows the low potential end of the secondary winding 35 of the intermediate frequency transformer 32 to be at ground potential both for direct and alternating currents. The cathode 50 of the device 49, shown 7 grounded in Figure 1-, is connected through a conductor 63'to a positive point on the bleeder resistor. l6 so chosen that the potential drop across the portion 'l6a.will bias the discharge device 49 to cut-off. The operation and regulatory ac- .7 tion ofthis vmodiimation a're in aILrespectsthe same as that of the arrangement shown in Figure 1 and willnot be again described.

In addition to accomplishing'the regulation of a supply source, my invention has the further advantage that the operation of the tuning indicator arrangement under control of the device 49 is materially improved. The operating grid of the device 49 is biased to cut-off, as previously explained, with the result that the positive potentials additionally applied to the control grid bythe'drop across the resistor 38 cause the device initially to operate upon the lower nonlinear portion of its grid-voltage anode-current characteristic curve. This characteristic curve has a sharp bend or knee near the cut-off point which'insures that small unidirectional potentials developed across the resistor 38 byfnoise. oscillations appearing in the signal channel 29 do not produce a material change in the anode space current of the device 49. The indication of the lamps 58 and 59 is therefore not changed by noise in the signal channel, as would be the case were the tuning indicator control tube so biased that a small anode space current flowed during the period when no signal is being received, and false indications from this source are thereby greatly reduced or eliminated.

I wish it clearly understood that wherever the expression radio frequency amplifier shall appear in the claims appended to this description, the expression shall include those amplifiers which amplify frequencies above the range of audibility as, for example, amplifiers of inter-, mediate frequencies.

- While I have shown particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto since different modifications may be, made both in the arrangement of the circuit and of the apparatus described. I, of course, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent oi'the United States, is:

1. The combination, in a signaling system, of a source of signal impulses, means connected to said source and including an electron discharge device for amplifying said signal impulses, a second electron discharge device, means connecting said second discharge device to said first device to operate said second device in response to the output of said first device, a source of potential having a terminal electromotive force for supplying space current individually to said discharge devices, means individually connecting said devices to said source, means responsive to the average strength of said signal impulses for controlling the gain and the average space current of said amplifying means, and means for additionally controlling said last-named discharge device by said last-named means in a manner to vary equally but in opposite sense the magnitude of the space currents consumed by each of said devices from said second-named source whereby said terminal electromotiveforce is maintained substantially constant.

2.'The combination, in a radio receiver, of a radio frequency amplifier having an input and an output circuit, a source of radio frequency electromotive force connected to' said input circuit, an auxiliary electron discharge device, a source of current connected to supply individual space currents'to said amplifier and to said device and'having a terminal electromotive force, (5'

andf'means. forfmaintaining said; terminal electromotive force substantially constant-,saidmgeansincluding a pair of re'ctifiersr associatediWith. the

out-put, circuitof said amplifier and arranged. to.

III

simuitaneously change, in opposite. sense; the magnitude of. the space currents 'of; said amplifier,:a:nd% said; device in response'to' a change in. theystrengt-hz of;the radio frequency. electromo tiv foizcepf: saidv first-named source;

31-32. rnqcombination .a radio frequency amplifier. havingan input circuit including; a*' control gridand; having an output circuit, a source: of radio: frequency electromotive force connected. to said,='inputcircuit, an auxiliary electron: discharge device :havingran' input circuit including a controltgrid, .a. scurceof current connected to; sunply. individual; space currents to said. amplifier andi tosaid: devicez andl havinga terminal electromotive force; and; means: for maintaining said terminal:- electromotive force' substantially constaiit; said: means including a pair of rectifiers connected' to: the output circuit of: saidgamplifiercand arranged to; develop individually unidirectional: electromotive forces from: the radio frequency current. appearing in said output circuit, saidi unidirectional: electromotive forces being applied to bias respectively the control grid of" said amplifier and said device in a manner simultaneously to change: in opposite sense the magnitude of' the space current of said amplifierla'nd' said device its response to av change: in strength of the radio frequency el-ectromotive force or said first-named source;

4 In a signaling system having. electron discharge devices individually receiving space current from a source having. a terminal potential variable upon variations in current flowing therefromjthemethodz' of maintaining. substantially constant the terminal potential of said source which consists in individually supplying said deviceswit'h currents from said source, converting a'signal potential to a control potential, applying said control potential to the control grid of" a first of said electron discharge devices in a manner to bias the control grid of said device toward cut-off; converting another portion of said signal potential to. asecond control potential, and applying said second control potentialto the control grid of a second of said electron discharge devices in a manner to bias the control grid of .said. second device away from cut-oil,

whereby the total current taken from said source by said device, and consequently said: terminal potential, tends to be more constant.

5. The combination, in a signal receiver,'of a plurality of amplifiers connected in succession with respect to signal currents transmitted through said receiver, a source of operating potentialfor said amplifiers, each of said amplifiers drawing varying amounts of current from said source in accordance with the intensity of signals received in said receiver, the output povidual to each of said amplifiers for supplying operating currentthereto from said source'the out.-

put potential of saidsource being. variable in response to. variations incurrent supplied thereby,

and. means responsive to changes in the average:

operating current supplied to. a first of said amplifiers substantially equal and opposite tothat supplied 'to the other, of said amplifiers whereby the-output. potential-of said source is maintainedsubstantially constant.

7. In a signaling system, the combination of strength, means: including.- an electron discharge device: for amplifying, said signals, means. in.-

eluding a second electron -discharge device for indicating a,- conditiorr of. said amplified signals, means connecting said;seconddevice. for operation. inresponse to. the output. of said first device, a sourcev of, space current having a terminal potential subject to variation: uponvariation. in current flowing from said ,.source,. means for supplyingspace currents from said source to saiddevices; means,.for maintaining substantially constant said: terminal potential, said lastnamed means: being responsive to the average strength of amplified. signals to vary the magnitudeof the.spaoelcurrentflowing. in each of said discharge devices, thespacecurrentof a first of said? devices varying. substantially equally and c ppositel'y.to. that .of the other of said devices.

' 8.-.The. combination, in a signaling system, of a source' of. signals having varying average strength, means including. anamplifier connect- .a source: of, signals;;having' a varying average ed to, said. source for amplifying said signals,

" means responsive to the average strength of amplified? signals for controlling and maintaining substantially constant the output of said amplifier as said signals vary in strength, said control means producing, variations in the space currentofsaidamplifier in proportion to changes of" signal strength;' means for supplying space current to'said amplifier, the potential at which said spacepurrent is supplied being subject to undesiredtvariations dependent upon the magni: tude'of said space current supplied, an electron dischargeydevice; means; for connecting said 'de vice tooperatdiriresponse to the output of said amplifier; and means for maintaining substantially' constant th'e'space current supplied by said space current supply means thereby to maintain said potential consta-nt said last-named means including said electron discharge device, and means responsive tethe average strengthof amplified signals for-varying the space current of said discharge device-substantially equally with but in adirection opposite to changes in the space current of said amplifien 95 a radio": receiving: system, the combination of tunable meansfor receiving signals having a varying; average". strength; means includ ing 'an electrondischargadevice for amplifying said signals,z'meansl for controlling the gain of said amplifying. means to maintain substantially constant thezoutput of said; amplifying means as saidf signals vary inwstrength', means including a secondi electron. discharge device for indicating the average strengthioff amplified signals, means connecting: said: indicating-2 means to operate in response: to the outputmfisaidi amplifying means tosprovidei'a ni indication: as the accuracyof tuning: of." said". tunable means" to said signal, means having: a: terminal potential for." supplying. space current: through separaterindividualrpaths to said devices, said potential being subject to variation upon variation in current flow from said last means and means for maintaining said terminal potential substantially constant, said lastnamed means being responsive to the strength of amplified signals for changing the space current of said last-named device equally with but in a direction opposite to changes in space current of said first-named device.

10. The combination in a radio receiver, of a number of signal stages and a tuning indicating stage, a source of operating potential common to all of said stages and subject to voltage variations upon variations in current flowing therefrom, means to vary the bias of all of said stages in response to the intensity of received signals, said means tending to vary the current in each of said stages, certain of said signal stages tending to operate undesirably upon voltage variations of said source, and means to prevent such undesired operation comprising means to increase current in said tuning indicating stage in response to said bias variation when current in said signal stages decreases, whereby variations in total current flowing from said source are reduced and the constancy of potential of said source is increased suificiently to eliminate said undesired operation.

11. The combination, in a superheterodyne radio receiver having signal stages and a tuning indicating stage, one of said signal stages including a local oscillator, of a source of operating potential common to all of said stages including said oscillator and subject to voltage variations upon variations in current flowing therefrom, the operating frequency of said oscillator being subject to variation upon variation in voltage supplied thereto from said source, means to vary the bias of certain of said stages in response to the intensity of received signals, said means tending to vary the current in each of said certain stages, and means to prevent said frequency variation comprising means to increase current in said tuning indicating stage in response to r said bias variation when current in said signal stages decreases, whereby variations in total current flowing from said source are reduced and the constancy of potential of said source is increased sufficiently to eliminate said frequency variation.

12. The combination in a radio receiver, of a number of signal stages and a tuning indicating stage, a source of operating potential common to all of said stages and subject to Voltage variations upon variations in current flowing therefrom, certain of said signal stages tending to operate undesirably upon said voltage variations, means to operate said tuning indicating stage from a signal stage to indicate maximum intensity 01 a received signal, means to vary the bias and the amplification of said signal stages in responsev to intensity of received signals, said last means tending to vary the current in said stages, and means to prevent such undesired operation comprising means to increase current in said tuning indicating stage in response to said bias variation when current in said signal stages decreases, whereby variations in total current flowing from said sources are reduced and the constancy of potential of said source is increased sufficiently to eliminate said undesired operation.

13. The combination in a radio receiver, of a number of signal stages and a tuning indicating stage, a source of operating potential common to all of said stages and subject to voltage variations upon variations in current flowing therefrom, means connecting said tuning indicating stage through an individual path to said source, certain of said signal stages tending to operate undesirably upon voltage variations of said source, means to vary the bias of all of said stages in response to the intensity of received signals, said last means varying the current and amplification in said signal stages, and means to prevent such undesired operation comprising means to increase the current flowing individually to said tuning indicating stage in response to said bias variation when current in said signal stages decreases, whereby variations in total current flowing from said source are reduced and the constancy of potential of said source is increased sufficiently to eliminate said undesired operation.

NORTON F. SHOFSTALL. 

